Two new pregnane glycosides from the root of Cynanchum auriculatum

Two new pregnane glycosides (1 and 2), together with four known ones (3- 6), were isolated from the roots of Cynanchum auriculatum Royle ex Wight (Asclepiadaceae). On the basis of detailed spectroscopic analysis and chemical method, the structures of new compounds were characterized to be metaplexigenin 3-O-β-D-cymaropyranosyl- (1→4)-α-L-diginopyranosyl-(1→4)-β-D-cymaropyranoside (1), metaplexigenin 3-O-α-L-diginopyranosyl-(1→4)-β-D-cymaropyranoside (2). All the isolated compounds (1-6) were tested for their in vitro inhibitory activity against the growth of human colon cancer cell lines HCT-116. Compounds 5 and 6 showed significant cytoxicities with IC₅₀ values of 43.58 µM and 52.21 µM.